Our studies over the last 2 and a half years have lead to significant breakthroughs in. our understanding of genotype-phenotype relationships in fragile X syndrome. We have discovered a significant translation problem in the conversion of mRNA into FMR1 protein (FMRP), which begins in the premutation range. Significant elevation in. mRNA levels abo"e controls are seen in males and females with the premutation. For premutation carriers who are significantly affected, mRNA levels may be up to 10 times normal and associated with a mild FMRP deficit. Executive function deficits are usually present in males with the premutation and a subgroup of these males who are older than 50 years demonstrate a cerebellar tremor associated with brain atrophy and a slowly progressive neurocognitive decline. These problems may be related to additive genetic effects and/or elevated mRNA levels. We do not yet know the prevalence of these neurological problems in older males with the premutation, or whether these problems may also occur in older females with the premutation. We also have preliminary evidence that autism in association with fragile X syndrome may be related to background gene effects. Our competitive renewal will focus on both of these problems: the association of autism and fragile X syndrome, and the emerging neurological phenotype in. older carriers with the premutation. We will study these problems within the format of our family study design (40 families per year) which provides controls within the family and allows an analysis of background gene effects with the pedigree analysis statistical approach from our collaborators Drs. Danuta Loesch and Richard Huggins at La Trobe University in Melbourne, Australia. We will utilize state of the art autism diagnostic tools including the Autism Diagnostic Interview (ADI-R) and the Autism Diagnostic Observation scale (ADOS-G) in addition to a family questionnaire to assess the extended autism phenotype. We will expand the family studies to consistently include grandparents and their siblings to better understand the aging process in carriers with neurological and neuropsychological assessments. Volumetric MRI studies will be done on older carriers with and without tremors and controls and all phenotypic findings will be correlated with FMR1 gene studies including mRNA, FMR1 protein, COG repeat number, methylation status, and activation ratio. In addition to the FMR1 gene studies, we will assess additional alleles, in collaboration with Gerard Schellenberg, Ph.D., including the serotonin receptor (5-HTT), and the GABA receptor (GABRB3) which are associated with autism, and ApoE and tau haplotypes associated with neurodegeneration.